java Lucene 中自定义排序的实现

Lucene中的自定义排序功能和Java集合中的自定义排序的实现方法差不多,都要实现一下比较接口. 在Java中只要实现Comparable接口就可以了.但是在Lucene中要实现SortComparatorSource接口和ScoreDocComparator接口.在了解具体实现方法之前先来看看这两个接口的定义吧.
SortComparatorSource接口的功能是返回一个用来排序ScoreDocs的comparator(Expert: returns a comparator for sorting ScoreDocs).该接口只定义了一个方法.如下:
Java代码
/**
* Creates a comparator for the field in the given index.
* @param reader - Index to create comparator for.
* @param fieldname - Field to create comparator for.
* @return Comparator of ScoreDoc objects.
* @throws IOException - If an error occurs reading the index.
*/
public ScoreDocComparator newComparator(IndexReader reader,String fieldname) throws IOException
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/**
* Creates a comparator for the field in the given index.
* @param reader - Index to create comparator for.
* @param fieldname - Field to create comparator for.
* @return Comparator of ScoreDoc objects.
* @throws IOException - If an error occurs reading the index.
*/
public ScoreDocComparator newComparator(IndexReader reader,String fieldname) throws IOException
/**
* Creates a comparator for the field in the given index.
* @param reader - Index to create comparator for.
* @param fieldname - Field to create comparator for.
* @return Comparator of ScoreDoc objects.
* @throws IOException - If an error occurs reading the index.
*/
public ScoreDocComparator newComparator(IndexReader reader,String fieldname) throws IOException
该方法只是创造一个ScoreDocComparator 实例用来实现排序.所以我们还要实现ScoreDocComparator 接口.来看看ScoreDocComparator 接口.功能是比较来两个ScoreDoc 对象来排序(Compares two ScoreDoc objects for sorting) 里面定义了两个Lucene实现的静态实例.如下:
Java代码
//Special comparator for sorting hits according to computed relevance (document score).
public static final ScoreDocComparator RELEVANCE;
//Special comparator for sorting hits according to index order (document number).
public static final ScoreDocComparator INDEXORDER;
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//Special comparator for sorting hits according to computed relevance (document score).
public static final ScoreDocComparator RELEVANCE;
//Special comparator for sorting hits according to index order (document number).
public static final ScoreDocComparator INDEXORDER;
//Special comparator for sorting hits according to computed relevance (document score).
public static final ScoreDocComparator RELEVANCE;

//Special comparator for sorting hits according to index order (document number).
public static final ScoreDocComparator INDEXORDER;
有3个方法与排序相关,需要我们实现 分别如下:
Java代码
/**
* Compares two ScoreDoc objects and returns a result indicating their sort order.
* @param i First ScoreDoc
* @param j Second ScoreDoc
* @return -1 if i should come before j;
* 1 if i should come after j;
* 0 if they are equal
*/
public int compare(ScoreDoc i,ScoreDoc j);
/**
* Returns the value used to sort the given document. The object returned must implement the java.io.Serializable interface. This is used by multisearchers to determine how to collate results from their searchers.
* @param i Document
* @return Serializable object
*/
public Comparable sortValue(ScoreDoc i);
/**
* Returns the type of sort. Should return SortField.SCORE, SortField.DOC, SortField.STRING, SortField.INTEGER, SortField.FLOAT or SortField.CUSTOM. It is not valid to return SortField.AUTO. This is used by multisearchers to determine how to collate results from their searchers.
* @return One of the constants in SortField.
*/
public int sortType();
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/**
* Compares two ScoreDoc objects and returns a result indicating their sort order.
* @param i First ScoreDoc
* @param j Second ScoreDoc
* @return -1 if i should come before j;
* 1 if i should come after j;
* 0 if they are equal
*/
public int compare(ScoreDoc i,ScoreDoc j);
/**
* Returns the value used to sort the given document. The object returned must implement the java.io.Serializable interface. This is used by multisearchers to determine how to collate results from their searchers.
* @param i Document
* @return Serializable object
*/
public Comparable sortValue(ScoreDoc i);
/**
* Returns the type of sort. Should return SortField.SCORE, SortField.DOC, SortField.STRING, SortField.INTEGER, SortField.FLOAT or SortField.CUSTOM. It is not valid to return SortField.AUTO. This is used by multisearchers to determine how to collate results from their searchers.
* @return One of the constants in SortField.
*/
public int sortType();
/**
     * Compares two ScoreDoc objects and returns a result indicating their sort order.
     * @param i First ScoreDoc
     * @param j Second ScoreDoc
     * @return -1 if i should come before j;
     * 1 if i should come after j;
     * 0 if they are equal
     */
    public int compare(ScoreDoc i,ScoreDoc j);
    /**
     * Returns the value used to sort the given document. The object returned must implement the java.io.Serializable interface. This is used by multisearchers to determine how to collate results from their searchers.
     * @param i Document
     * @return Serializable object
     */
    public Comparable sortValue(ScoreDoc i);
    /**
     * Returns the type of sort. Should return SortField.SCORE, SortField.DOC, SortField.STRING, SortField.INTEGER, SortField.FLOAT or SortField.CUSTOM. It is not valid to return SortField.AUTO. This is used by multisearchers to determine how to collate results from their searchers.
     * @return One of the constants in SortField.
     */
    public int sortType();
看个例子吧!
该例子为Lucene in Action中的一个实现,用来搜索距你最近的餐馆的名字. 餐馆坐标用字符串"x,y"来存储.
Java代码
package com.nikee.lucene;
import java.io.IOException;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.index.TermDocs;
import org.apache.lucene.index.TermEnum;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.ScoreDocComparator;
import org.apache.lucene.search.SortComparatorSource;
import org.apache.lucene.search.SortField;
//实现了搜索距你最近的餐馆的名字. 餐馆坐标用字符串"x,y"来存储
//DistanceComparatorSource 实现了SortComparatorSource接口
public class DistanceComparatorSource implements SortComparatorSource {
private static final long serialVersionUID = 1L;
// x y 用来保存 坐标位置
private int x;
private int y;
public DistanceComparatorSource(int x, int y) {
this.x = x;
this.y = y;
}
// 返回ScoreDocComparator 用来实现排序功能
public ScoreDocComparator newComparator(IndexReader reader, String fieldname) throws IOException {
return new DistanceScoreDocLookupComparator(reader, fieldname, x, y);
}
//DistanceScoreDocLookupComparator 实现了ScoreDocComparator 用来排序
private static class DistanceScoreDocLookupComparator implements ScoreDocComparator {
private float[] distances; // 保存每个餐馆到指定点的距离
// 构造函数 , 构造函数在这里几乎完成所有的准备工作.
public DistanceScoreDocLookupComparator(IndexRe